Compilers: Overview

Compilers and InterpretersCompilation

Translation of a program written in a source language into a semantically equivalent program written in a target languageOversimplified view:*CompilerError messagesSourceProgramTargetProgramInputOutput

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Compilers and Interpreters (contd)Interpretation

Performing the operations implied by the source programOversimplified view:*InterpreterSourceProgramInputOutputError messages

Compilers and Interpreters (contd)Compiler: a program that translates an executable program in one language into an executable program in another language

Interpreter: a program that reads an executable program and produces the results of running that program

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The Analysis-Synthesis Model of CompilationThere are two parts to compilation:

Analysis Breaks up source program into pieces and imposes a grammatical structureCreates intermediate representation of source programDetermines the operations and records them in a tree structure, syntax treeKnown as front end of compiler*

The Analysis-Synthesis Model of Compilation (contd)Synthesis Constructs target program from intermediate representation Takes the tree structure and translates the operations into the target programKnown as back end of compiler

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A language-processing system*PreprocessorCompilerAssemblerLinkerSkeletal Source ProgramSource ProgramTarget Assembly ProgramRelocatable Object CodeAbsolute Machine CodeLibraries andRelocatable Object Files

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AnalysisIn compiling, analysis has three phases:

Linear analysis: stream of characters read from left-to-right and grouped into tokens; known as lexical analysis or scanningHierarchical analysis: tokens grouped hierarchically with collective meaning; known as parsing or syntax analysisSemantic analysis: check if the program components fit together meaningfully*

Lexical analysisCharacters grouped into tokens.

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Syntax analysis (Parsing)Grouping tokens into grammatical phrasesCharacter groups recorded in symbol tableRepresented by a parse tree

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Syntax analysis (contd)Hierarchical structure usually expressed by recursive rulesRules for definition of expression:

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Semantic analysisChecks source program for semantic errorsGathers type information for subsequent code generation (type checking)Identifies operator and operands of expressions and statements

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Phases of a compiler*

Symbol-Table ManagementSymbol table data structure with a record for each identifier and its attributesAttributes include storage allocation, type, scope, etcAll the compiler phases insert and modify the symbol table

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Intermediate code generationProgram representation for an abstract machineShould have two properties

Easy to produceEasy to translate into target programThree-address code is a commonly used form similar to assembly language

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Code optimization and generationCode Optimization

Improve intermediate code by producing code that runs fasterCode Generation

Generate target code, which is machine code or assembly code*

The Structure of a Compiler (8)*

Parse treeAbstract Syntax Tree w/ AttributesNon-optimized Intermediate CodeOptimized Intermediate Code

Target machine code

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The Grouping of PhasesCompiler front and back ends:

Front end: Analysis steps + Intermediate code generationDepends primarily on the source languageMachine independentBack end: Code optimization and generationIndependent of source languageMachine dependent*

The Grouping of Phases (contd)Compiler passes:

A collection of phases is done only once (single pass) or multiple times (multi pass)Single pass: reading input, processing, and producing output by one large compiler program; usually runs fasterMulti pass: compiler split into smaller programs, each making a pass over the source; performs better code optimization*

Compiler-Construction ToolsSoftware development tools are available to implement one or more compiler phases

Scanner generatorsParser generatorsSyntax-directed translation enginesAutomatic code generatorsData-flow engines*

Thank You*

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